2536 - Comparison of Scanning Beam Proton Therapy vs. Photon IMRT in Patients with Locally Advanced Non-Small Cell Lung Cancer

Purpose/Objective(s): As interest in the potential dosimetric benefits of Scanning-Beam Proton Therapy (SPT) over intensity-modulated radiation therapy (IMRT) or volumetric modulated arc therapy (VMAT) continues to grow, we aim to provide an updated analysis comparing these treatment modalities in patients with stage III non-small cell lung cancer (NSCLC). This update is timely as advances in radiation delivery and immunotherapy have reshaped treatment. Utilizing institutional data from 2018 to 2024, we have evaluated dosimetry, clinical outcomes, and toxicity. The primary endpoint was to compare treatment-related toxicity, specifically lung and esophageal toxicity, between SPT and IMRT/VMAT. Secondary endpoints included dosimetric differences and survival outcomes (progression-free and overall survival). This study seeks to address the ongoing question of whether proton therapy offers a clinical advantage over photon-based IMRT/VMAT in the management of locally advanced NSCLC.

Materials/Methods: We retrospectively identified 95 consecutive patients with stage III NSCLC treated at our institution between 2018 and December 2024 (63 SPT, 32 IMRT) with institutional review board approval. Patients were included if they received definitive radiation therapy with SPT or IMRT/VMAT. All treatments incorporated advanced planning techniques with rigorous quality assurance protocols. To focus on clinically significant toxicity, we analyzed Grade 3+ pneumonitis, as it represents severe and life-threatening cases requiring medical intervention. Statistical comparisons were performed using the Chi-square test for categorical variables and Welch’s t-test for continuous variables.

Results: Patient characteristics were comparable between the photon and SPT cohorts. Results are summarized in the table below.

Conclusion: This updated analysis of SPT and IMRT in the treatment of stage III NSCLC shows that SPT delivers lower doses to normal lung tissue compared to IMRT. While SPT demonstrated dosimetric advantages, no statistically significant differences were observed in toxicity or survival outcomes. The study is limited by its retrospective nature and sample size, warranting further prospective evaluation.